Laptop's Batteries Auto-disconnect?

Charging a battery to 100% or discharging it to 0% damages the battery, decreasing its capacity as it ages. This is the reason some of the batteries on older laptops only last 5 minutes.

http/batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

I've seen two strategies used by manufacturers to avoid this damage. The first is the one you mention - stop charging when it hits 100%, and don't recharge it until it drops to 90% or 95%. Probably the worst thing you could do to the battery was immediately top it off to 100% again the moment it dropped to 99%. The old Toshiba laptops were pretty bad about this, topping off the battery every few minutes. Most of those Toshiba batteries needed to be replaced within a year. Back in those days, we would remove the battery from the laptop once it was fully charged, and insert it only when we needed to use it without AC power.

The second method is to understate the battery's capacity. That is, the label on the battery will say 48 Wh, but Windows will detect it as a 43 Wh battery. The extra 10% is used to provide a buffer at the high and low ends. That is, when Windows reports the battery is charged to 100%, it's actually only charged to 95%. When it reports the battery is at 0%, it's actually at 5%. Sometimes this is accomplished by tricking Windows into thinking it's a 43 Wh battery. Sometimes it's done by telling Windows the battery is already worn and only has 43 Wh of capacity left. This is the same strategy employed by electric and hybrid cars. Most of them limit battery charges to the middle 50%-60% of the battery's actual capacity.

Every modern laptop I've seen uses one of these strategies to protect battery longevity. I think in the past manufacturers abused this as a way to increase sales of replacement batteries. But with the move towards internal batteries, I think they are now more interested in making sure the battery works well for many years.